Pulsed Surface Discharge Research Articles

Underwater shock wave induced by pulsed discharge on water

Plasmas on liquids have provided significant applications in material, environmental, and biological sciences. The mechanisms of these chemical reactions in liquids have been primarily described by the plasma–liquid interactions and convection by an electrohydrodynamic flow. Although shock waves play a significant role in radical formation, agitation and cell destruction, not much information is available on underwater shock waves induced by the surface discharge on water. In this study, an underwater shock wave generated by the pulsed surface discharge on water using the laser shadowgraph method has been demonstrated. The results reveal that the shock wave generated by the discharge on water was transmitted into the water. The mean velocity of the shock wave reached 1.7 km s−1. The results indicate that the surface discharge accelerates the reaction in the water by the combined action of the underwater shock wave and the plasma reaction at the air–water interface. The results are expected to aid in the understanding the mechanisms of existing applications, such as decomposition, synthesis, and sterilization.

Extrusion of a nanosecond surface discharge plasma near a dielectric ledge

The presence of a dielectric ledge along the pulse discharge propagation led to a redistribution of the pulsed surface (plasma sheets) discharge glow. Discharge glow on the surface without the ledge, was uniform and lasted no more than 200 ns. Two plasma channels with increased glow intensity were observed near the rectangular ledge placed in the discharge area. The duration of these longitudinal plasma channels increased and lasted for about 0.9 μs (at a voltage of 25 kV and a density of 0.03 – 0.18 kg/m3 ). A nine-frame nanosecond camera recorded the evolution of the plasma glow. The dynamics of the flow induced by the pulse surface discharge was recorded using a high-speed shadow imaging during 40-50 μs after the ignition of the discharge.

Nanosecond discharges in a non-stationary flow around an obstacle

The purpose of the work is to study the effect of a pulsed surface discharge (plasma sheet) on the transverse flow upon its initiation in an unsteady gas-dynamic flow in a channel with an obstacle on the wall. Also a comparison with the effect of a pulsed volume discharge under similar conditions was studied. The dynamics of the blast waves propagating from the separation zone behind the obstacle after self-localization of the discharge plasma there is investigated.

Repetitively pulsed gas discharges: memory effect and discharge mode transition

Repetitively pulsed gas volume and dielectric surface discharges have gained growing attention because of peculiar and exciting physics phenomena, high efficiency, high reactivity, and potential to obtain conventionally unachievable plasma properties. Nevertheless, incomplete understanding of fundamental mechanisms renders the repetitively pulsed discharge far less predictable and controllable, where the inherent memory effect and the discharge mode transition are universal challenges. In this topical review, the authors will explore the macroscopic characteristics of the gas gap breakdown and the surface flashover, state-of-the-art mechanisms and dominant agents of discharge memory effects, operation regimes and transitions of the discharge mode, and how waveform parameters affect the pulsed discharge properties. Challenges and potential approaches for further understanding the memory effect and the discharge mode transition in the repetitively pulsed discharge are discussed.

Validation of the local thermodynamic equilibrium at a local current concentration area of positive pulsed surface discharge plasma on water

Pulsed surface discharge on water has been given attention as a water purification technology and material synthesis method. The contribution of this study is to clarify the plasma state of a positive pulsed surface discharge on water. Although the pulse width of the current dramatically decreased with an applied voltage ranging from 10 to 20 kV under a conductivity of water of 1 mS cm−1 and a water depth of 2 mm, the plasma state in the vicinity of the needle electrode was a local thermodynamic equilibrium (LTE) state. Validation of the LTE was performed by the McWhirter criterion. On the other hand, the propagating discharge along the water surface was supposed to be in non-LTE state. Consequently, the pulsed surface discharge on water was in mixed states of LTE and non-LTE.

Simulation of voltage/current waveforms and contact area of pulsed surface discharge on water

Propagation of a surface discharge on water is evaluated using simulation results of the voltage/current waveforms and discharge contact area. Voltage/current waveforms are calculated using an exponential function which assumes the resistance of water decreases with increasing discharge contact area. A conductive disk having a given potential is used to model the discharge contact area and the temporal variation of the radius of the disk is discussed as the discharge propagation. The calculation in the current field is replaced by a calculation of the electrostatic field using the similarity between current and electrostatic fields. The calculation of the electrostatic field is conducted by a charge simulation method. The discharge phenomena are classified into two stages which are the breakdown of needle-to-water gap and the surface discharge propagation on water. The electrostatic field calculation at needle-to-water gap is performed to determine the initial discharge contact area. Expansion of the contact area in the creepage direction, is evaluated by the electric field calculation at the edge of the conductive disk. The expansion terminates when the field becomes lower than 26 kV/cm. The velocity of the expansion increases with the applied voltage. The maximum contact radius increases with decreasing conductivity of water under the same applied voltage. The tendency of simulation results of the expansion of the contact area are consistent with the previous observation results of the discharge propagation.

UV Radiation of High-Voltage Multi-Electrode Surface Discharge in Gaseous Medium

UV radiation of high-voltage pulsed multispark surface discharge in atmospheric-pressure air in the spectral range of 200–380 nm was investigated. The discharge was a sequence of microplasma objects with a specific energy deposition of ~1 kJ/cm3 and electron density of 1017 cm–3. Copper and stainless steel were used as the electrode materials. It is found that lines of atoms and ions of the electrode material dominate in the discharge UV spectrum. The UV radiation intensity was measured using the actinometry technique. The UV radiation efficiency relative to the energy deposited in the discharge is found to be ~1%.

Bactericidal effect of cold plasma on microbiota of commercial fish balls

Abstract This study evaluated the bactericidal effect of cold plasma on three spoilage bacteria isolated from commercial fish balls: Psychrobacter glacincola 38–1, Brochothrix thermosphacta 38–2, and Pseudomonas fragi 38–8. Bacterial suspensions were treated by pulsed discharge plasma (PDP, 50 Hz, 3.0 L/min) and gas phase surface discharge plasma (GPSDP, 75 Hz, 6.5 L/min). The inactivation behavior was closely related to the peak discharge voltage, initial bacterial concentration, and exposure time. After treatment with GPSDP for 300 s (12.8 kV), a reduction of 6.87, 4.81 and 3.32 log10 CFU/mL was observed for 38–1, 38–2 and 38–8, respectively. However, when the voltage of PDP reached 20 kV, inactivation was initiated. P. glacincola 38–1 was the most sensitive to plasma treatment. After 4-min treatment with PDP or 30-s treatment with GPSDP, the 38–1 (approximately 105 CFU/mL) were completely inactivated. A Weibull model and a modified Whiting-Buchanan model provided a good fit for the survival curves, with R2 ≥ 96%. After plasma treatment, deformation and rupture of bacterial cells were observed by SEM and TEM; the leakage of cellular contents was also observed by TEM. The oxidation by active particles (H2O2 and O3) was the primary mechanism of bacterial inactivation exerted by GPSDP. PDP acted synergistically through physical penetration and chemical oxidation, which combined to lead to cell death. Industrial relevance Commercial fish balls are popular in China, and they are usually transported and stored in the cold chain (mainly frozen environment). Although efficient cold chain can reduce the rate of microbial changes in fish balls, there are still limits of cold chain. The inevitable fluctuations in temperature during cold chain provide conditions for the attachment and growth of cold-tolerant bacteria that may lead to spoilage of commercial fish ball. The proposed research gives insight into how to control microbial contamination of commercial fish balls. Cold plasma treatment proved to be effective at killing the three bacteria tested, and the inactivation achieved by GPSDP was far superior to that achieved by PDP treatment. Dynamic fitting of a mathematical model was performed to describe the inactivation behaviors. This also provides a basis for predicting the inactivation of microorganisms. The study offers firm theoretical foundation and practical guidance for the application of cold plasma in the quality control of commercial fish balls, and further contributes to the safety of foods in cold chain.

A New Evaluation Method of Contact Area at Interface Between Pulsed Surface Discharge and Water

The authors propose a new method for evaluating the contact area of a surface discharge on water by analyzing the resistance of water solution. This method supplements optical observations of light emissions and the Schlieren method. The contact area was modeled as a disk electrode, and the theoretical resistance of water was calculated under the assumption of a mutual similarity between the current and electrostatic fields. A simulated electrostatic field was calculated using a common charge-simulation method. The experimental values of the resistance of water were obtained by dividing the measured voltage drop at water by the measured current. The contact area evaluation was performed by comparing the experimental and theoretical resistance values. The contact area increases with increasing the applied voltage and is practically independent of water depth.

Fluid and hybrid modeling of nanosecond surface discharges: effect of polarity and secondary electrons emission

In this paper, we report on results from a computational investigation of nanosecond pulsed surface discharges of positive and negative polarity using a 2D fluid and fluid-Monte Carlo simulation. The streamers propagate along the dielectric surface in an asymmetric actuator geometry. The essential difference between the streamers of positive and negative polarities is observed. For positive polarity the intense sheath region is formed near the surface having high values of the electric field. The negative streamer has a lower field at the streamer front and in the sheath region. The disparity between the positive and negative surface streamers increases when electron Monte Carlo simulation is used that treats the energetic secondary electrons in a fully kinetic way. We also found that for a negative polarity applied to the exposed electrode, a thin layer of precursor electrons ahead of a streamer is formed having a shape of a narrow protruding needle. The effect is attributed to the production and trapping of fast secondary electrons in the narrow anodic sheath region.

Study on the characteristics of barrier free surface discharge driven by repetitive nanosecond pulses at atmospheric pressure

Nanosecond pulsed plasma has an enormous potential in many applications. In this paper, the characteristics of barrier free nanosecond pulsed surface discharge are investigated by the use of an actuator with a strip-strip film electrode configuration, including the effect of electrode width and the gap distance on the plasma morphology and electrical characteristics at atmospheric pressure. It was found that it is relative easier to generate a quasi uniform discharge with a thinner electrode width and a smaller gap distance. The underlying physical mechanism was also discussed. Besides that, the influence of airflow on repetitive pulsed surface discharge was examined. By comparing to the discharge produced by two different pulse waveforms in airflows, we found that the discharge driven by a faster pulse behaves more stable. Finally, a model was developed to analyze the interaction of the airflow and the discharge channels.

Study of Hydrogen Peroxide Generation by Water Surface Discharge

This paper reports on experimental studies of chemical activities of pulse discharge plasmas generated in contact with water surface. The pulse discharge propagated in the form of streamer channels along the water surface. Hydrogen peroxide was used as a chemical probe for the evaluation. Point-to-plane electrode geometry and pulse high voltage of positive polarity was used for the experiments. A magnetic pulse compression pulsed power modulator was employed. Effects on discharge characteristics of the air gap distance between the high voltage electrode tip and water surface as well as solution conductivity were determined. The discharge characteristics were identical for different gap distances and solution conductivities; meanwhile, the streamer channels' length and their light emissions on water surface were changed with conductivity. No significant effect of gap distance between the needle tip and water surface on the formation of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> by the pulsed water surface discharge was determined. However, the formation rates of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> decreased with increasing medium conductivity.

Resistance Models Applied to the Return Stroke Phase of Negative Pulsed Surface Discharges in Air

The energy deposition during the return stroke phase of a pulsed surface discharge is driven by the electrical circuit and the electrical properties of the discharge. To control these factors, a parametric study is performed with varying the circuit parameters, for different discharge lengths and voltages between -19 to -26 kV. The electrical characteristics of the discharge are then simulated using different plasma resistance models, which assume a time-varying resistance: the Toepler model, the Rompe-Weizel model, and the Vlastós model. The model parameters are optimized to fit the experimental results. The analysis shows that for long pulses obtained with large inductance, the three models fare equally well, since the discharge resistance is mainly constant during the pulse. In low-inductance cases, the Toepler model leads to larger errors during the initial current pulse, whereas the Rompe-Weizel and Vlastós models describe with a good agreement the experiments. The discharge resistance evolves during the first 300 ns, then remains mostly constant until the end of the pulse. The constant part of the resistance gives the surface-averaged conductivity of the discharge, which increases linearly with the linear energy dissipated in the discharge. Finally, theoretical estimates of the varying resistance parameters are in fair agreement with the parameters obtained while fitting the experiments, in particular in the Rompe-Weizel case. These findings can be used to estimate the channel resistance of a pulsed surface discharge, and to help optimizing the high-voltage circuit.

Measurement of the impulse produced by a pulsed surface discharge actuator in air

The pulsed surface discharge in atmospheric pressure air generates a shock wave, thereby transferring an impulse to the surrounding gas. The aim of this work is to measure this impulse, using implementation of a plasma actuator based on linear surface discharges of length up to 10 cm, and of linear energy in a range 0.1–0.5 J cm−1. The shock wave generated by the discharge is visualized using a pulsed schlieren system and the impulse is measured with a dedicated balance. These measurements are correlated with 1D numerical simulations of pulsed energy depositions in a perfect gas. Experiments show that the discharge generates a cylindrical shock wave that travels at sonic speed after a few tens of microseconds, and produces an impulse that varies from 1 to 4 mN s m−1 and scales linearly with the linear energy density. This linearity agrees with the numerical simulations when 9.5% of the energy dissipated in the discharge is assumed to heat the gas. Overall, to produce a time-averaged force similar to the one achieved by dielectric barrier discharge (DBD) actuators, 2 to 3 times more power is required. However, surface discharge actuators do not saturate, and thus can induce time-averaged forces one or two orders of magnitude above DBD when pulsed at several hundreds of hertz.

Investigation of the interaction of a shock wave with the zone of a pulsed surface discharge in a rectangular channel

This study concerns the effect of the zone of a plane surface energy deposition on a gas-dynamic flow with a shock wave of M = 2.3–2.7 in a channel with a rectangular cross section. The source of the pulsed energy is a distributed sliding nanosecond discharge that develops in an approximately 1-mm-thick layer on a surface of 100 × 30 mm2. The results of a 3D numerical simulation of the problem on the basis of the Navier-Stokes equations for a compressed gas are presented and compared with the experimental shadow images.

The development of turbulence behind a shock wave front moving in an inhomogeneous region

We have studied the formation of vortex structures and the development of turbulence behind the front of a shock wave with Mach number M = 1.5–3.0 moving along a near-wall gas layer excited by a nano-second pulsed transverse surface discharge within 40–500 μs after initiation. Schlieren images of the flow are compared to the results of two-dimensional numerical simulations based on the Navier-Stokes equations and a pulsed energy deposition model.

Study of shock-wave flows in the channel by schlieren and background oriented schlieren methods

The results of recording gas flow in a shock tube by the schlieren and background oriented schlieren (BOS) methods after initiating a pulsed (surface or volume) discharge are presented. Simultaneous recording of the flow field by the two methods allows a complete qualitative and quantitative analysis of the shock-wave processes resulting from the interaction of a pulse discharge with high-velocity flow. The vector displacement field of the BOS method was determined by the cross-correlation method. The density field was obtained by solving the Poisson equation with special boundary conditions. It was shown that the BOS method yields a good quality map of the flow structure that corresponds to the classical schlieren method and provides reliable quantitative results except in areas of high gradients. A modification of the BOS method was proposed and tested to measure the density jump at the shock-wave front. Recording was performed at an angle to the plane of the wave front. Various Schemes of processing of digital flow images were tested. The proposed method provides a resolution of large density gradients at the shock-wave front. The obtained quantitative results are consistent with the calculated values.

Gas-dynamic phenomena accompanying shock-wave interactions with the cooling plasma of a pulsed surface discharge

Gas-dynamic phenomena accompanying shock-wave interactions with the cooling plasma of a pulsed surface discharge

Mechanisms and Predictors of Insulator Degradation and Erosion Produced by Pulsed High-Current Surface Discharges

The mechanisms and predictors of insulator degradation and erosion by pulsed high-current surface discharges are presented and discussed. Erosion and degradation depend on the insulator material, the electrode material, the ambient gas, and the presence of UV stabilizers in, or on the surface of, the insulator. Insulator degradation is the result of material decomposition into conductive metal or carbon species and is measured by a decrease in the surface breakdown voltage. Insulator erosion is measured by the material's mass loss. The performance of a large group of ceramic, polymeric, and elastomeric materials tested with graphite and molybdenum electrodes is presented in this investigation. The insulators are exposed to repetitive 300-kA 20-mus-long surface discharges. Tests are performed in atmospheric air and pure nitrogen. Various methods to rank insulators in terms of holdoff voltage degradation, mass erosion, and holdoff voltage conditioning (HVC) using the material's thermochemical properties are presented and discussed. HVC is characterized by an initial increase in surface holdoff voltage. The ranking method developed by the authors characterizes the insulator according to the holdoff degradation resistance (HDR), mass vaporization coefficient (MVC), and HVC figures of merit calculated by the material's thermochemical properties. The investigation also shows the relationship between the HDR, MVC, and HVC figures of merit.

On the possibility of controlling transonic profile flow with energy deposition by means of a plasma-sheet nanosecond discharge

A way of effectively affecting the gasdynamic structures of a transonic flow over a surface by means of instantaneous local directed energy deposition into a near-surface layer is proposed. Experimental investigations into the influence of a pulsed high-current nanosecond surface discharge of the “plasma sheet” type on gas fast flow with a shock wave near the surface are carried out. The self-localization of energy deposition into a low-pressure region in front of the shock wave is described. Based on this effect, a facility for automated energy deposition into a dynamic region bounded by the moving shock front can be designed. The limiting value of the specific energy deposition on the surface in front of the shock wave is found. With the help of the direct-shadow method, an unsteady quasi-two-dimensional discontinuous flow arising when a plasma sheet is initiated on the wall in a flow with a plane shock wave is studied. By numerically solving the two-dimensional nonstationary equations of gas dynamics, the influence of the energy of a pulsed nanosecond discharge, which is applied in the frequency regime, on the aerodynamic characteristics of a high-lift profile is investigated. It is ascertained that the energy delivered to the gas before the closing shock wave in a local supersonic region that is located in the neighborhood of the profile contour in zones extended along the profile considerably decreases the wave drag of the profile.